Tadpole's Promise

The other night my son brought home a library book called Tadpole's Promise by Jeanne Willis.
I was kind of excited to read this story at first, thinking it was about a romantic young love, portraying how even those that are the most different can find love in unusual circumstances.  A love that will blossom if given enough time and faith, etc.  Even though I give off somewhat of a cynical vibe at times, I really am a total optimist at heart, and a complete sucker for romance.  So, you can imagine my disappointment when that is not at all how this story ends (story transcribed in italics below for anyone that hasn't read it and may be intrigued).

I'm not really sure how to feel about this story, or, in particular, the ending. And to make matters worse, it is quickly becoming one of CJ's favorite stories. Part of me thinks "well, it's pretty realistic, right?" and another part of me can't let go of what a disappointment it is.  I mean, I can understand reading a book as an adult full of reality and not so happy endings.  I totally get that.  But in a kids book?  Aren't they supposed to be full of happy endings and messages of hope in all circumstances in an effort to preserve their innocence and the vast amount of possibilities, hopes, and dreams still contained within their hearts and minds?  Aren't we supposed to still be sending the message 'anything is possible if you put your heart and mind to it' at this stage? 

I don't know.  I'm lost on this one.  Maybe I'm not really interpreting the metaphor correctly?  I thought about it from the standpoint of a woman, or anyone really, in a relationship that has been lied to and/or abused.  The woman being the caterpillar, and the man being the tadpole.  They start out young, full of hope and promise.  But inevitably, he changes in ways that may or may not be beyond his control.  There is always the promise that things will be better, things will be different, or things will go back to the way they were.  But more often than not, it never turns out that way.  The one that has been betrayed goes away, blossoms to become a beautiful butterfly, but still can't seem to let go of the relationship and the hope that it can be what she dreams it to be.  So she goes back, and is consumed by the relationship to the point where she no longer even exists as what she once was or as the butterfly she became - and the one in the relationship doing so much damage remains completely oblivious to their destruction and wonders where it all went wrong and where the girl he fell in love with went.

 It's the only explanation that seems understandable, or even relateable to me (can you tell I have some issues), but I still don't understand the ever daunting question:  Why a kid's book?  As in, let's take away hope, replace it with the harsh realities of the world in an effort to protect against broken hearts?  What is the point of having a heart if it's too hard to break anyway? Seems to be kind of a paradox to the age old saying "Tis better to have loved and lost, than never to have loved at all."

Reading too far into it?  Looney tunes?  I won't blame you if you say yes.  Just curious as to what others have to say about it, and looking for a little insight other than my own.

(It's a fairly short story, so if you are intrigued, the story follows below).

"Where the willow meets the water, a tadpole met a caterpillar. They gazed into each other's tiny eyes... and fell in love. She was his beautiful rainbow, and he was her shiny black pearl. 
'I love everything about you,' said the tadpole.
'I love everything about you,' said the caterpillar. 'Promise you'll never change.'
'I promise,' he said.
But as sure as the weather changes, the tadpole could not keep his promise.  Next time they met, he had grown two legs.
'You've broken your promise,' said the caterpillar.
'Forgive me,' begged the tadpole.  'I couldn't help it.  I don't want these legs... All I want is my beautiful rainbow.'
'All I want is my shiny black pearl.  Promise me you'll never change,' said the caterpillar.
'I promise,' he said.
But sure as the seasons change, the next time they met, he had grown arms.
'That's twice you've broken your promise,' cried the caterpillar.
'Forgive me,' begged the tadpole. 'I could not help it.  I do not want these arms... All I want is my beautiful rainbow.'
'And all I want is my shiny black pearl.  I will give you one last chance,' said the caterpillar.
But as sure as the world changes, the tadpole could not keep his promise.  The next time they met, he had no tail.
'You have broken your promise three times, and now you have broken my heart,' said the caterpillar.
'But you are my beautiful rainbow,' said the tadpole.
'Yes, but you are not my shiny black pearl.  Good-bye.'  She crawled up the willow branch and cried herself to sleep.
One warm moonlit night, she woke up.  The sky had changed.  The trees had changed.  Everything had changed... except for her love for the tadpole.  Even though he'd broken his promise, she decided to forgive him.
She dried her wings and fluttered down to look for him.  Where the willow meets the water, a frog was sitting on a lily pad.
'Excuse me,' she said. 'Have you seen my shiny black...'
But faster than she could say 'pearl,' the frog leapt up and swallowed her in one great gulp.
And there he waits...
thinking fondly of his beautiful rainbow...
... wondering where she went." - Jeanne Willis

What do you think?